Logical Decisions - Classweb

Thus, proportionally increasing the weight for Cost as we increase
its range correctly compensates for the change and keeps equally
preferred alternatives equally ranked.
Top Down Vs. Bottom Up. An issue related to ranges and
weights is whether preferences in a goals hierarchy should be
assessed from the top down or the bottom up.
The top down approach is to assess the relative weights of the
highest level goal first and then to do lower level assessments to
allocate each goal’s weight among its members. The bottom up
approach is to first assess the relative weights of the lowest level
measures within each lowest level goal and then to do higher
level assessments to establish the relative weights of higher level
goals.
While both approaches are possible in LDW, the bottom up
approach is preferred. This is because the top down approach
makes it difficult to think about the measures below a goal when
assessing its relative weight.
When assessing the weight for a high level goal, it is tempting to
think about the global significance of the goal’s name rather than
the specific measures (and associated ranges) included under the
goal. This can lead to too much weight assigned to a measure
with a very narrow range or too little weight assigned to a
measure with a wide range.
In the bottom up approach, the decision makers will have thought
about the measures under a goal before assessing the weight of
the goal itself. This should lead to more reasonable weight
assessments for the higher level goals.
An even better approach is to use representatives (page 34) to
assess each goal’s weight indirectly. Its easier to think about the
range and importance of a single measure than to think about the
whole set of measures represented by a goal.
Ranges and Weights in LDW. The tradeoff method is the only
weight assessment method in LDW that automatically
compensates for changes in measure ranges. This is because the
tradeoff method uses pairs of equally preferred alternatives and
computes weights based on the measure ranges to make their
utilities come out equal.
9-54 Section 9 -- In Depth